(CNN) – President Barack Obama said Friday that the U.S. military and his security team were looking at a “wide range of options” on how to respond to the chemical weapons attack in Syria, but he added that any U.S. action would not involve sending troops or waging a long-term campaign.

Going it alone against the Syrian government is not what President Barack Obama wants, U.S. Secretary of Defense Chuck Hagel said Friday.

But that scenario is looking more and more likely.

A day earlier, the United States’ closest ally, Great Britain, backed out of a possible coalition. A U.N. Security Council meeting on Syria ended in deadlock, and in the U.S. Congress, doubts about military intervention are making the rounds.

Skeptics of military action are invoking Iraq, where the United States government under President George W. Bush marched to war based on a thin claim that former dictator Saddam Hussein was harboring weapons of mass destruction.

Opponents are conjuring up a possible repeat of that scenario in Syria, though the intelligence being gathered on the use of WMDs in Syria may be sounder.

An attack on President Bashar al-Assad may prove to be politically unpopular. The American public is not enthused by the prospect.

“Only 25% of the American people support military action in Syria,” former U.S. ambassador to the United Nations Bill Richardson told CNN’s Piers Morgan Thursday.

Convincing evidence

To shake off the specter of the Iraq war, the public needs convincing that chemical weapons were used and that al-Assad’s regime was behind it.

“You have to have almost incontrovertible proof,” Richardson said.

It’s there, said Arizona Sen. John McCain, and will be visible soon. He thinks comparisons with Iraq are overblown and that doubts are unfounded.

“Come on. Does anybody really believe that those aren’t chemical weapons — those bodies of those children stacked up?” he asked Morgan.

Al-Assad’s government has claimed that jihadists fighting with the opposition carried out the chemical weapons attacks on August 21 to turn global sentiments against it.

McCain doesn’t buy it.

“The rebels don’t have those weapons,” he said.

The president also needs to assure Congress that a possible intervention would not get out of hand, said Democratic Rep. Chris Van Hollen from Maryland.

“The action has to have a very limited purpose, and the purpose is to deter future use of chemical weapons,” he said.

Alone or together?

After British lawmakers on Thursday voted down a proposal on military intervention, a senior U.S. official, speaking on condition of anonymity, told CNN that going it alone was a real prospect.

“We care what they think. We value the process. But we’re going to make the decision we need to make,” the official said.

A former director of the CIA believes Obama would face off with al-Assad alone.

“I can’t conceive he would back down from a very serious course of action,” retired Gen. Michael Hayden told CNN’s Wolf Blitzer.

Hagel’s response to the vote was more diplomatic.

The United States respects the results, Hagel told journalists in Manila, the Philippines. “Every nation has a responsibility to make their own decisions.”

The U.S. will continue to consult with the British government and still hope for “international collaboration.”

“Our approach is to continue to find an international coalition that will act together,” he said.

Haunted by Iraq

The parliamentarians in London shot down the proposal in spite of intelligence allegedly incriminating the government of President Bashar al-Assad.

Britain’s Joint Intelligence Committee has concluded it was “highly likely” that Syrian government forces used poison gas outside Damascus last week in an attack that killed at least 350 people, according to a summary of the committee’s findings released Thursday.

“There is no credible intelligence or other evidence to substantiate the claims or the possession of CW (chemical weapons) by the opposition,” Britain’s Joint Intelligence Committee concluded in a document released Thursday. “The JIC has therefore concluded that there are no plausible alternative scenarios to regime responsibility.”

A yes vote would not have sent the UK straight into a deployment.

Cameron had said his government would not act without first hearing from the U.N. inspectors and giving Parliament another chance to vote on military action.

But his opposition seemed reminded of the Iraq war.

“I think today the House of Commons spoke for the British people who said they didn’t want a rush to war, and I was determined we learned the lessons of Iraq, and I’m glad we’ve made the prime minister see sense this evening,” Labour Party leader Ed Miliband told the Press Association.

The no vote came after a long day of debate, and it appeared to catch Cameron and his supporters by surprise.

For days, the prime minister has been sounding a call for action, lending support to talk of a U.S.- or Western-led strike against Syria.

“I strongly believe in the need for a tough response to the use of chemical weapons, but I also believe in respecting the will of this House of Commons,” the prime minister said.

“I get that, and the government will act accordingly,” he said.

The government of France supports military intervention, if evidence incriminates the government of using poison gas against civilians.

But on Friday, President Francois Hollande told French newspaper Le Monde that intervention should be limited and not include al-Assad’s overthrow.

Letter from al-Assad

Before the vote, Syria’s government offered its own arguments against such an intervention. In an open letter to British lawmakers, the speaker of Syria’s parliament riffed on British literary hero William Shakespeare, saying: “If you bomb us, shall we not bleed?”

But the letter also invoked Iraq, a conflict justified on the grounds that Iraq had amassed stockpiles of chemical and biological weapons and was working toward a nuclear bomb — claims that were discovered to have been false after the 2003 invasion.

“Those who want to send others to fight will talk in the Commons of the casualties in the Syrian conflict. But before you rush over the cliffs of war, would it not be wise to pause? Remember the thousands of British soldiers killed and maimed in Afghanistan and Iraq, not to mention the hundreds of thousands of Iraqi dead, both in the war and in the continuing chaos.”

British Commons Speaker John Bercow published the letter.

UN deadlock

Lack of support for military intervention at the United Nations on Thursday was less of a surprise.

Russia, which holds a permanent seat on the Security Council, is one of Syria’s closest allies and is most certain to veto any resolution against al-Assad’s government that involves military action.

Moscow reiterated the stance Friday.

“Russia is against any resolution of the UN Security Council, which may contain an option for use of force,” Deputy Foreign Minister Gennady Gatilov said on Friday.

A closed-door Security Council meeting called by Russia ended with no agreement on a resolution to address the growing crisis in Syria, a Western diplomat told CNN’s Nick Paton Walsh on condition of anonymity.

U.N. weapons inspectors are now in Syria trying to confirm the use of chemical weapons. The inspectors are expected to leave the country by Saturday morning.

They are to brief U.N. Secretary-General Ban Ki-moon, who in turn, will swiftly brief the Security Council on the findings.

Congressional jitters

The president is facing doubts at home as well: More than 160 members of Congress, including 63 Democrats, have now signed letters calling for either a vote or at least a “full debate” before any U.S. action.

The author of one of those letters, Democratic Rep. Barbara Lee of California, said Obama should seek “an affirmative decision of Congress” before committing American forces.

More than 90 members of Congress, most of them Republican, signed another letter by GOP Rep. Scott Rigell of Virginia. That letter urged Obama “to consult and receive authorization” before authorizing any such military action.

Congress is currently in recess until September 9.

White House spokesman Josh Earnest said Obama was still weighing a potential response to the chemical weapons attacks.

The president has said that he is not considering a no-fly zone and has ruled out U.S. boots on the ground in Syria.